Archive for September, 2012

The SPURS work has renewed interest in the broader community in studying the ocean to better understand the global water cycle, heating and cooling of the oceans, and oceanic mixing.

Julian Schanze of Woods Hole Oceanographic Institution/MIT is about to complete his Ph.D. in physical oceanography under the supervision of Ray Schmitt. Julian and Ray are on the Knorr to study ocean salinity, the water cycle and mixing in the ocean.

Julian Schanze at work.

Raymond Schmitt on the Knorr.

For his Ph.D. project, Julian is trying to estimate how much mixing occurs in the ocean. For this, he is using satellite datasets on surface fluxes of heat and fresh water and a concept known as power integrals. This is a mathematically complex subject, so let’s avoid the technical details and consider it in simpler terms.

Consider that, broadly speaking, the Earth is heated near the equator and cooled near the poles. For the equatorial and polar regions to not heat up or cool down, respectively, the excess heat must be transported away from the equator and towards the poles through mixing. The same approach can be used for the water cycle (which creates salt differences) as well such as ocean density and other, let us say “weird” ocean variables. For example, oceanographers consider the “spiciness” of ocean water as a measure of how warm and salty it is. So Julian is doing something really cool and looking at not just at heat moving through the ocean, but density and spiciness fluctuations as well. These are directly related to vertical and horizontal mixing in the ocean.

The equations that govern these power integrals relate the production of heat and salt variance (in our example, heating at the equator and cooling at the poles) to the destruction of variance (mixing) in the interior ocean. However, Ray and Julian found something curious: Under the right circumstances, the ocean interior can produce density variance rather than destroy it. The reason for this is double diffusion or salt fingers. When warm, salty water is found atop cool, fresh water, heat is diffused faster than salt in the ocean, leading to the formation of cold and salty “salt fingers”. These salt fingers transport salt downward and can create sharp density gradients. The SPURS region is top heavy in salt and therefore a likely place to find salt fingers.

On this SPURS cruise, Julian is trying to extend his understanding of mixing in the oceans from theoretical studies to hands-on work with the data. He is hoping the data will help him constrain uncertainties in the global maps of the water cycle and the heat budget that he has assembled. But while the approach he has taken in his dissertation allows him to calculate the total sum of mixing in the ocean, it does not constrain where the mixing occurs. This is where instruments deployed in SPURS enter the picture. Some of the SPURS instruments specifically allow for mixing in the ocean interior to be estimated by recording miniscule changes in temperature, salinity, and velocities in the ocean. The Vertical Microstructure Profiler and several of the gliders equipped with similar technologies allow oceanographers to estimate mixing quite precisely.

Night deployment of Velocity Microstructure Profiler.

Sensor package on VMP.

On board, Julian is in charge of the Lowered Acoustic Doppler Profiler (LADCP), an instrument lowered on a wire that records horizontal velocities in the ocean by pinging sound waves off small particles that float in the water. This requires him to prepare the instrument for deployment, charge its batteries and process the data after the retrieval. The LADCP helps identify good sites for mixing by measuring where the velocity changes most rapidly with depth.

How did Julian get to be such an intelligent man? He tells me that at age seven, he moved close to the North Sea in Germany and became fascinated by the ocean. He soon became a keen sailor and decided to complete a four-year B.S./M.Sci. degree in oceanography at the University of Southampton in England. While his research has been largely focused on using satellite data to estimate the global water cycle (80-90 percent of which occurs over the ocean), he is thrilled at being able to go on a month-long research cruise to get in touch with the subjects he has been studying for the last 9 years. His fascination with satellite remote sensing and his research in oceanography are perfectly combined in NASA’s work on SPURS and the advent the Aquarius satellite, to measure sea surface salinity from space.

Everyone on Knorr believes that Julian has a stellar career in front of him!

The thermosalinograph (TSG) on Knorr is a shipboard instrument for measuring temperature and salinity of the near surface water . It is situated in a lab and receives a flow of water taken in near the bow and piped out near the stern.

Inlet and pump for the Knorr’s thermosalinograph. (Photo: Julius Busecke.)

It is quite an adventure going down to see the inlet for the TSG. You go to a storage locker in the bow, then down a long tunnel, then forward at the bottom of the ship. And you discover something cool when you get there. When Knorr was built, they put viewing ports in the bow. One could sit below the waterline in the very front of the ship and watch the ocean go by. Wow! They must have been really cool for watching bottlenose dolphins playing in the ship’s bow wave! Sadly, the viewing ports were sandblasted at some time in the past, and one can no longer see through the glass.

Start of downward journey to the thermosalinograph and the viewing port in the bow. (Photo: Julius Busecke.)

On a cheerier note, an Aquarius project led by Prof. Arnold Gordon of Lamont Doherty Earth Observatory has been focused on surface salinity and the global record provided by TSGs on research vessels and ships of opportunity (commercial vessels that carry scientific equipment and take automatic measurements that scientists then use for their research).

Phil and Julius are aboard Knorr for SPURS from Lamont to assure the quality of the TSG data and provide ongoing analysis of the surface salinity from various instruments, including Aquarius. Chief Scientist Ray Schmitt set a contest in motion for a free dinner in the Azores for the group that documents and collects a bottle sample of the highest salinity of this SPURS expedition (most likely at the ocean surface). Game on!

Julius at work.

Phil at work.

The closer we look at the ocean with increasingly sophisticated satellite and ship-based instrumentation, the less it looks like the textbook images of large-scale circulation gyres, and more of an assemblage of around 100-km-sized eddies. What role do these eddy “swirls” play in the overall climate system? And more specifically, how effective are eddies in stirring freshwater into the evaporative salty regimes of the subtropics? During the SPURS field program the TSG and hull-mounted Acoustic Doppler Current Profiler (ADCP) observations of ocean currents are used to map the eddy field, to ascertain their potential to compensate the excess evaporation. What we learn will be applied along with the Aquarius satellite ocean surface salinity data, to other areas of the ocean, to more fully grasp the impact of eddy dynamics on the marine hydrological system.

The Lamont team prepared for this expedition by inspecting the archival surface layer temperature and salinity in the SPURS region, collected by Voluntary Observing Ships and transits from past research expeditions to estimate the eddy flux of freshwater into the North Atlantic evaporative subtropics. What they found is encouraging: the ocean eddies very well may be the primary force in compensating the net regional evaporation. The seasonal cycle of the eddy effect seems to set the seasonal swings of the ocean surface salinity, not net evaporation. The SPURS expedition data along with the Aquarius satellite data provides a far more quantitative data set to pursue this topic.

SPURS experimental design and measurement methods, consisting of sensor-laden moorings with an array of autonomous instrumentation, provide a beautiful 3-D view of the ocean stratification and circulation as it evolves over time. The R/V Knorr’s high resolution TSG and ADCP, as well as the data stream from the Aquarius satellite, link together the data from all these assets, to fully capture the eddy field and ascertain its role in the larger scale system. It’s exciting to see the complex factors influencing ocean surface salinity coming into focus!

While we can guess what we might observe, being there to actually see the data as it rolls in allows for the building of understanding and thus adjustment of the experimental design to maximum return. The observations from the Knorr will expand our quantitative knowledge of how the ocean, and its field of eddies, are coupled to the sea-air flux of water. That is oceanographer speak for “this is awesome!”

The Research Vessel Knorr is a fantastically capable oceanographic research vessel. She has traveled over 2 million miles and explored all the major oceans in her around 40 years of service.

As a visiting oceanography research crew, we have our space on the ship, for which we have free run. We are mostly in the main labs, on deck, or in the mess (getting fed very well indeed!) Much of the ship is off-limits to personnel other than the crew. I asked for a tour so I could give you a quick view of some “hidden” portions of the ship that make everything work. The daily routine is for the scientists to request that the ship, with her propulsion, station-keeping, cranes, winches, and capstans, to go here, stop there, stay still, lift this, pick up that… and so on, with only vague appreciation of the engineering feats behind these daily miracles.

I was privileged to get a tour of Knorr’s engineering space from the Chief Engineer Steve Walsh. He has been with Woods Hole Oceanographic Institution and aboard the Knorr for many years and participated in the vessel’s complete refit in 1991.

In 1991, the ship was basically cut in two pieces and 34 feet were added to her mid-section. The new engine room was placed in the new section and the space freed up in the after section (the old engine room) is now used as a workshop, welding room, and scientific cargo space.

Knorr’s machine and welding shop.

Knorr still has the old engine order telegraph connected to the bridge.

At the noisy heart of the ship are the engines (3500 Series Caterpillar). These run the four generators that supply 600V energy for all the ship’s electrical needs (which are many). The voltage is stepped down for various different purposes to 480V, 220V, and 120V (like in your house). The generators drive electric motors for primary propulsion, thrusters, and supply power for air conditioning, refrigeration, cranes, winches, lighting, computing, navigation and the coffee machine. According to Steve the most critical elements by far are the air conditioning and the coffee machine. OK, he’s half-joking…but I know he is serious about the coffee machine!

One of the electric motors for propulsion.

Upper deck crane on R/V Knorr.

It seems to me like the Knorr is, in some ways, like my all-electric home back in Maryland. When the power goes out, it’s a hollow, dark, cold shell of a place. Except on Knorr, we have the power company living in the basement using diesel engines to run the generators to keep our lights on. And unlike my house, the Knorr can also get up and go wherever oceanography takes her and use a crane to pick up the garage and car (or 10,000-lb mooring anchors) to go along for the trip. Knorr has all the comforts of home, work, and play for our 33 days at sea. They are all in one awesome package. All powered by home-grown, engineer-maintained, electricity.

There are not many places in the open ocean that get their own special name as a “sea.” Most seas are what we call marginal seas – offshoots of the major ocean basins.

The Sargasso Sea, as a vast track of the western subtropical North Atlantic Ocean is known, has a special characteristic – something noted by Portuguese sailors for centuries and even visible from space. It is the home waters of Sargassum, a genus of brown macroalgae (seaweed) that inhabit the open ocean. The sea is named after the seaweed and it seems that small clumps are nearly always within sight of the ship (we have yet to see giant mats of the stuff in the SPURS region). Anyway, the Sargasso Sea is special because of a plant. Well, it is more complicated than that!

A patch of Sargassum at the surface (Photo: Julian Shanze.)

Sargassum, up close.

Closeup of Sargassum.

In my opinion, the really cool thing about Sargassum is that each clump can be a teeming ecosystem by itself. Several varieties of fish (e.g. Sargassum fish and flying fish), crabs , and nudibranchs live in close association with the weed. Each clump is a complex island of life floating free at the surface of the deep ocean. When you are out here in the vast emptiness of the open ocean, it is just hard to imagine how this intricate web of life came to be, survived, and actually thrives. Every time I am in the Sargasso Sea, it seems such a wonder.

A flying fish.

Barnacles on French glider recovered by Knorr.

We had spectacular sunset last night and I was reminded of the old adage: “Red sky at night, sailor’s delight. Red sky in morning, sailor’s warning.” Here we are still in proximity to Hurricane Nadine and is this saying true, or is it just an old wives’ tale? Like the answer to most questions, there is a web site for that. In fact I think it may be true for us; we are well south of the hurricane weather and forecasts have good weather for in days ahead.

Sunset sen from the Knorr.

An interesting sidebar to today’s blog topic is another kind of life we have found in great abundance at our SPUR study location. It was a mystery for a few days – we were seeing lots of floating microscopic reddish dusty particles. Some said it looked a little like sawdust (but where are the trees?), and some wondered whether it was floating dust from the Sahara. Well, thank goodness for the Web again. I discovered that it’s a bloom of an important nitrogen-fixing bacterium (Trichodesmium) also known as “sea sawdust.” It certainly reinforces the idea that a key to identification is a good description!

Trichodesmium in a bucket of sea water.

A Trichodesmium bloom in the Pacific Ocean seen from space.

Trichodesmium, it turns out, just loves these sea conditions – just as much as SPURS oceanographers love the North Atlantic salinity maximum!

After several weeks of your following my postings from the field, I thought it would be good to tell you a little about myself. Maybe that will help explain the weird wanderings of the blog or the subject matters I choose to write about.

Let’s start at the beginning: I grew up in Seal Beach, California, very near the ocean. It seems to me like I actually grew up on the sand and in the water. So, I am pretty well infused and enthused by the seas. This has driven me toward a broad knowledge of ocean subjects. I felt that drive vindicated when National Geographic Society tapped me as senior scientific consultant (pro bono) on their first ocean atlas project.

When did I decide to become an oceanographer? I was pretty interested in the field in middle and high school. Science seemed like where I was headed. Being a good student, I was able to get into the Massachusetts Institute of Technology. There, before I finished my freshman year, I fell in love with the Earth and Planetary Sciences Department. It was a short course in astronomy that got me hooked. They really reeled me in when I realized that Earth science was just then being revolutionized by the ideas of plate tectonics and that oceanographers at MIT were bringing back the first pictures of hydrothermal vents on the mid-ocean ridges. There was not much in the way of undergraduate education in oceanography at MIT, but lots of good basic math, physics, geology, geophysics, and research opportunities. I can date myself by recalling the glorious summer of 1976, when I stayed in Boston for the bicentennial and to do my undergraduate research project on data from Lake Ontario. The lake wasn’t salty, but it was a great little laboratory for oceanography ideas! That summer truly set me on course to pursue physical oceanography as a career (and provided my first publication with Prof. John Bennett: “A simple model of Lake Ontario’s coastal boundary layer,” in Journal of Physical Oceanography, July 1977). Most scientists remember their first publication quite fondly and I am no exception!

Graduate school at University of Washington was filled with studies and expeditions. It took me six years to get my Masters and a Doctor of Philosophy in Physical Oceanography degrees. My dissertation was on eddies in the North Atlantic Ocean. It turned out that eddies deep below the surface of the ocean can carry water across the ocean from quite distant places and arrive in the Sargasso Sea with evidence of their origins from as far afield as the Labrador Sea, the Antarctic Circumpolar Current, or the Mediterranean Sea. The idea that these origins and travels could be traced using salinity measurements was intoxicating (in a nerdy sort of a way) for a young oceanographer. I loved the data collection part of the project; being part of the right team with the right equipment in the right place at the right time to make some discovery that would move science forward. The ocean is still virtually unexplored, so every well-planned expedition has potential for great discovery. Once oceanographic expedition science is in your blood, it’s hard to give it up! I found a great opportunity for doing more expedition research by moving to Australia in 1983. The country had expanded ocean research greatly at that time due to advent of the Law of the Sea and extended Exclusive Economic Zones. Sometimes, timing is everything!

In Australia, I became engrossed in studies of the western tropical Pacific Ocean circulation and in the planning for the World Ocean Circulation Experiment (WOCE). By the end of the 1980s, the former had seen me on many expeditions near exotic tropical islands and the latter looked to be the oceanography opportunity of the 1990s. I moved back to the U.S., still working on the same projects, but with a new home base. By the mid-1990s I was the US WOCE Program Scientist in Washington, D.C. That involved organizing scientific plans, budgets, and logistics for the largest mapping of ocean waters ever undertaken, involving voyages across the globe for nearly a decade. I was bitten by the vision of global ocean observing provided by WOCE and still suffer from that fever.

Eric, giving a talk at the Consortium for Ocean Leadership.

When the opportunity arose in 1997 to lead NASA’s Physical Oceanography Program, I had the right stuff: solid experience with the ocean, ocean programs in DC, ocean researchers in general, and virtually no heritage at all with satellite oceanography (but NASA said I could learn that on the job!)

It was in my first days at NASA HQ that I began energizing NASA’s drive toward measuring ocean salinity from space. All I had to do was enable those with the knowledge and skill to realize the dream (it certainly was not a new idea) – and prove to NASA that it was both possible and useful. And here we are today. I am back out on a research vessel, doing what I love, with Aquarius, our ocean surface salinity instrument, on orbit overhead and a whole community of scientists curious about ocean salinity and the global water cycle. It’s one small victory for this man, and one giant leap for physical oceanography.

Eric, taking a break on an Argo float box after a long day of blogging at sea.